While each of the first three fights were fantastic showcases of top-tier boxing, Pacquiao has been the dominating force in the series. With wins in the last two bouts, and what should have been a win in the first, the Marquez series helped propel Pacquiao into the pound-for-pound star we see today.
However, it will also prove to be his demise, as Marquez will pull off a massive upset that will shock the boxing world on Saturday.
How will he pull it off? Here is a look at how Marquez will shock the world and come away with an upset over Pacquiao.
He Will Take Pacquiao the Distance
If you want to look for an overarching reason, Pacquiao is coming into this bout on a losing streak rather than on a winning high. He's suffered from a recent inability to finish fights.
His fight against Timothy Bradley was the most egregious example of Pacquiao's recent struggles. Two of the judges had Bradley winning each of the last three rounds, while one had him winning five of the last six.
What's more, Pacquiao has not won via a knockout in his last five fights—a stretch that dates back all the way to his TKO of Miguel Cotto in November 2009.
If you want to look for a Pacquiao fight that finished before the 12th round, you'll have to have to go back to his dominant 2009 win over Ricky Hatton. Knocking Hatton out in the second round made Pacquiao seem like the best pound-for-pound boxer in the world.
Considering recent history, and that each of the three previous fights went the distance, it stands to reason that this one will too.
Look for Marquez to pull a Bradley and start overtaking Pacquiao on the judges' scorecards as the fight wears on.
Opponent Familiarity Will Haunt Pacquiao
Pacquiao's strength when first facing an opponent is that they underestimate how powerfully he punches.
It's one thing to hear about the hallowed power.
It's another thing to stand toe-to-toe with one of the most powerful punchers in boxing history and try to hold ground.
Marquez will not have that problem. He's learned over the course of three fights how to defend against Pacquiao's punches—and done so the hard way.
Pac-Man knocked Dinamita down three times in their first fight—in the first round alone.
However, it's been a different story in the two most recent fights. Pacquiao knocked down Marquez in the third round in the second fight, but did not do so in the last 21 rounds of the boxers' trilogy.
Marquez's resilience against Pacquiao comes with familiarity. This was especially demonstrated in the third fight when Pacquiao's ability to connect with strong, effective power punches went way down.
Anyone who has watched the Filipino star knows he's never been the best at adjusting his fighting style. By using his familiarity with Pacquiao and taking advantage of his mediocrity at adjusting, Marquez will be able to win key rounds and come away with the victory.
The Commitment Chasm
Questioning Pacquiao's commitment to the sport has become a popular trope in the months leading up to the fight.
Ted Lerner, a writer who has known Pacquiao for his entire career, openly questioned the 33-year-old's passion in an interview with ESPN's Nigel Collins:
I don't think the spark is there anymore. He's found religion, politics and business, and now has many other interests away from the ring. Clearly that special edge that made Manny a once-in-a-generation phenomenon has faded considerably and will continue to fade if he continues to fight.
Meanwhile, Marquez is a fighter. He's been in the sport since 1995 and has no other commitments.
Granted, it's a circumstantial reason to pick a boxer in a fight. But, Pacquiao's commitment has been questioned in recent years, including by some in his own camp. The Pac-Man has gone through a rigorous training program, but eight weeks won't make up for the lost time.
Many consider Pacquiao the best pound-for-pound fighter in the world, but we'll find out on Saturday how far he's truly fallen.